This invention relates to dispenser cathodes for use in diffuse gas discharge tubes and more particularly to a dispenser cathode which employs an emitting surface parallel to ion flow.
Dispenser cathodes have been employed for a number of years and generally use a tungsten-base material. The modern dispenser cathode consists of a strongly bonded, continuous metallic phase of a refractory metal or metals such as tungsten. The tungsten cathodes are interspersed uniformly with an emitting material. The porous metal matrix acts as reservoir from which the emitting material can diffuse to the surface to maintain an active layer and consequently provide a low work function surface for the thermionic emission of electrons. This definition excludes oxide coated cathodes, pure metal emitters and thoriated tungsten. Certain dispenser cathodes employ a porous tungsten structure and are impregnated with a molten mixture of barium oxide and other compounds which enhance the emission and lower the work function. The density of the tungsten structure can be varied from 75% to 85% of theoretical by volume.
As indicated, modern dispenser cathodes are well known and for a review and examples of such dispenser cathodes reference is made to an article entitled MODERN DISPENSER CATHODES by J. L. Cronin, published in I.E.E.E. Proceedings, Volume 128, Part 1, No. 1, February 1981, pages 19-32. This article explains the various types of dispenser cathodes which are employed in the prior art as well as the various materials utilized in such cathodes. Thus as one can ascertain, the dispenser cathode has been in existence for quite some time and essentially has been employed in gas discharge tubes such as high power thyratrons and so on. There have been many problems associated with dispenser cathodes as evidenced by examples given in the above noted reference. A major problem associated with such cathodes is caused by ion back bombardment of the dispenser cathode which occurs during tube operation. The bombardment of the cathode structure by ions will deplete the surfaces of the cathode of emitting material. This of course results in low emission until a new active layer migrates up from the bulk. Thus in normal tube operations, ion bombardment of the cathode which is a consequence of the charge transfer in the discharge will deplete the cathode of emitting material and hence substantially reduce the operating capability and life of the cathode and therefore the tube.
It is an object of the present invention to provide a cathode emitting surface which substantially eliminates the detrimental effects of ion back bombardment.